LIN28 is an RNA-binding protein that is expressed in many developing tissues. It can block let-7 (Mirlet7) microRNA processing and help promote pluripotency. We have observed LIN28 expression in the developing mouse neural tube, colocalizing with SOX2, suggesting a role in neural development. To better understand its normal developmental function, we investigated LIN28 activity during neurogliogenesis in vitro, where the succession of neuronal to glial cell fates occurs as it does in vivo. LIN28 expression was high in undifferentiated cells, and was downregulated rapidly upon differentiation. Constitutive LIN28 expression caused a complete block of gliogenesis and an increase in neurogenesis. LIN28 expression was compatible with neuronal differentiation and did not increase proliferation. LIN28 caused significant changes in gene expression prior to any effect on let-7, notably on Igf2. Furthermore, a mutant LIN28 that permitted let-7 accumulation was still able to completely block gliogenesis. Thus, at least two biological activities of LIN28 are genetically separable and might involve distinct mechanisms. LIN28 can differentially promote and inhibit specific fates and does not function exclusively by blocking let-7 family microRNAs. Importantly, the role of LIN28 in cell fate succession in vertebrate cells is analogous to its activity as a developmental timing regulator in C. elegans.
"Furthermore, miRNAs stimulate RNA-silencing complexes to induce degradation, destabilization, and/or translational inhibition of target mRNAs (Bartel, 2009; Guo et al., 2010; Huntzinger and Izaurralde, 2011) and are seemingly involved in almost all cellular events, including the determination of cell fate (Ebert and Sharp, 2012; Friedman et al., 2009). In the developing mammalian CNS, various miRNAs participate in the control of neural stem cell self-renewal, proliferation, and differentiation (Balzer et al., 2010; Cimadamore et al., 2013; Li and Jin, 2010; Naka-Kaneda et al., 2014; Neo et al., 2014; Qureshi and Mehler, 2012; Shibata et al., 2011; Visvanathan et al., 2007; Yoo et al., 2009; Zhao et al., 2009). This study identifies miR-153 as a regulator of the initiation of gliogenesis in the developing CNS. "
"This is important in the regulation of differentiation (15,16), especially as LIN28 and let-7 form a regulatory negative feedback loop (17). Interestingly, let-7-independent translation regulation by LIN28 occurs before the let-7-dependent step in Caenorhabditis elegans (18,19). LIN28 enhances translation, in a let-7-independent manner, of mRNAs important for cell growth in embryonic stem cells via the recruitment of RNA helicase A to polysomes (20–22). "
[Show abstract][Hide abstract] ABSTRACT: LIN28 function is fundamental to the activity and behavior of human embryonic stem cells (hESCs) and induced pluripotent stem
cells. Its main roles in these cell types are the regulation of translational efficiency and let-7 miRNA maturation. However, LIN28-associated mRNA cargo shifting and resultant regulation of translational efficiency upon
the initiation of differentiation remain unknown. An RNA-immunoprecipitation and microarray analysis protocol, eRIP, that
has high specificity and sensitivity was developed to test endogenous LIN28-associated mRNA cargo shifting. A combined eRIP
and polysome analysis of early stage differentiation of hESCs with two distinct differentiation cues revealed close similarities
between the dynamics of LIN28 association and translational modulation of genes involved in the Wnt signaling, cell cycle,
RNA metabolism and proteasomal pathways. Our data demonstrate that change in translational efficiency is a major contributor
to early stages of differentiation of hESCs, in which LIN28 plays a central role. This implies that eRIP analysis of LIN28-associated
RNA cargoes may be used for rapid functional quality control of pluripotent stem cells under manufacture for therapeutic applications.
Nucleic Acids Research 05/2014; 42(12). DOI:10.1093/nar/gku430 · 9.11 Impact Factor
"Lin-28 is an important regulator of let-7 miRNAs, and it has a functional role in organismal growth and metabolism, tissue development, somatic reprogramming and cancer (reviewed in
). During in vitro differentiation of mouse embryonic carcinoma cells to neural and glial fates, Lin-28 can alter the cell fate independently of let-7; in addition, overexpression of Lin-28 increases neurogenesis in the same cell types
. In vitro and in vivo experiments have demonstrated that Lin-28 regulates the translation and stability of a large number of mRNAs including cell cycle regulators, splicing factors, metabolic enzymes and RNA-binding proteins
[Show abstract][Hide abstract] ABSTRACT: One of the promises in regenerative medicine is to regenerate or replace damaged tissues. The embryonic chick can regenerate its retina by transdifferentiation of the retinal pigmented epithelium (RPE) and by activation of stem/progenitor cells present in the ciliary margin. These two ways of regeneration occur concomitantly when an external source of fibroblast growth factor 2 (FGF2) is present after injury (retinectomy). During the process of transdifferentiation, the RPE loses its pigmentation and is reprogrammed to become neuroepithelium which differentiates to reconstitute the different cell types of the neural retina. Somatic mammalian cells can be reprogrammed to become induced pluripotent stem cells (iPSCs) by ectopic expression of pluripotency inducing factors such as Oct4, Sox2, Klf4, c-Myc and in some cases Nanog and Lin-28. However, there is limited information concerning the expression of these factors during natural regenerative processes. Organisms that are able to regenerate their organs, could share similar mechanisms and factors with the reprogramming process of somatic cells. Herein, we investigate the expression of pluripotency inducing factors in the RPE after retinectomy (injury) and during transdifferentiation in the presence of FGF2.
We present evidence that upon injury, the quiescent (p27Kip1+/BrdU-) RPE cells transiently dedifferentiate and express sox2, klf4 and c-Myc along with eye field transcriptional factors and display a differential up-regulation of alternative splice variants of pax6. However, this transient process of dedifferentiation is not sustained unless FGF2 is present. We have identified lin-28 as a downstream target of FGF2 during the process of retina regeneration. Moreover, we show that overexpression of lin-28 after retinectomy was sufficient to induce transdifferentiation of the RPE in the absence of FGF2.
These findings delineate in detail the molecular changes that take place in the RPE during the process of transdifferentiation in the embryonic chick, and specifically identify Lin-28 as an important factor in this process. We propose a novel model in which injury signals initiate RPE dedifferentiation, while FGF2 up-regulates Lin-28, allowing for RPE transdifferentiation to proceed.
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